Process for dewaxing oils



May 25, 1937. u. B. BRAY E1- AL 2,081,732

PROCESS FOR DEWAXING' OILS Fild Nov. 6, 1933 J v INVENTORS Ulric BBray j? Dona/d5 Carr bx By Q j ATTORNEY.

Patented May 25, 1937 UNITED STATES PATENT OFFICE PROCESS FOR DEWAXING OILS Application November 6, 1933, Serial No. 696,892

Claims.

The present invention relates to a process for separating asphalt and wax from oils in the pro.- duction of lubricating oil. More particularly, it relates to a process for separating wax from wax containing oils in a plurality of stages.

Processes are now known for dewaxing oils for the production of lubricating oils wherein liquefied normally gaseous hydrocarbon solvents or diluents, such as liquid propane are employed. In such processes the wax containing oil is commingled with the diluent under a pressure sufficient to maintainthe diluent in the liquid state at room temperatures. If the oil contained asphaltic impurities, these Will precipitate in the presence of the diluent and settle to the bottom of the decanter after which the oil solvent solution containing the wax is decanted from the settled asphaltic impurities. The pressure on the solution is then gradually reduced to permit vaporization of the diluent which causes the remaining solution of oil and diluent to be chilled and thus precipitate the wax. Temperatures of approximately -40 F. may be obtained by the evaporation of the diluent under reduced pressure. The precipitated wax is separated in the presence of the remaining diluent by filtration, settling or centrifuging. If sufiicient diluent is not present in the oil subsequent to refrigeration to give a good separation of the oil solvent solution from the precipitated wax, additional quantities of diluent are added.

However, in such processes involving the use of liquefied normally gaseous hydrocarbon diluents such as liquid propane, difficulty has been experienced in dewaxing the oils, particularly light refined oils containing high wax contents to low pour points. We have observed that wax containing oil contains two types of Waxes, i. e. a heavy, hard wax of high melting point which precipitates and settles readily from the solution of oil and diluent and a second soft, light wax of low melting point which does not precipitate nor settle as readily. The waxes of low melting point present in oils have a solubility in such solvents or diluents as propane at dewaxing temperatures of approximately 40 F. or lower which is considerable. When substantial amounts of propane diluent are employed, this may result in the solution of sufiicient wax to amount to a difference in pour point of to 39 F. between the depropanized dewaxate, i. e. the dewaxed oil, and the same dewaxate when rendered free of light wax impurities.

If such oils are dewaxecl in the presence of low volumetric ratios of propane to oil, serious difficulties arise in attempting to filter efliciently. The filter rates on the basis of the viscous oil are very low and the back pressures across the filter cake are high and furthermore the filter cake must be repeatedly washed to bring the recovery of oil up to the theoretical yield. With some oils the concentration of wax is very high and the aforementioned difiiculties are more pronounced when attempting to dewax such oils. This is particularly true in dewaxing oils which have previously been heavily treated with extractive solvents, such as liquid sulphur dioxide employed to remove the aromatic components in the oil. As a consequnce of this removal of oil fractions, the wax which is sparingly soluble in the fractions removed or the extract phase of the extraction is concentrated in the raflinate phase or the desirable lubricating oil fractions.

On the other hand, if a sufiiciently high propane oil ratio is used to give economical filter rates and good yields, the pour points of the oils are raised 10 to 30 F. due to the solubility of the wax in the propane.

It is, therefore, an object of our invention to improve upon the aforesaid process for dewaxing oil employing liquefied normally gaseous hydrocarbon solvents such as liquid propane.

A particular object of our invention resides in removing substantially all of the wax in the oil in the presence of a liquefied normally gaseous hydrocarbon solvent and to produce lubricating oils of low pour points.

It is another object of our invention to provide a process which will facilitate removal of wax from oils without serious disadvantage in filters.

We have discovered that the solubility of wax in the coexistent lubricating oil itself is much lower than in such liquefied normally gaseous hydrocarbon diluents as liquid propane or similar dewaxing solvents. In fact this phenomenon is what makes the older method of cold pressing oils at the relatively high temperatures of approximately 10 to 20 F. practicable. Cold pressing of undiluted oils would be a very effective method of wax separation were it not for the severe limits placed on theprocess by the viscosity of the oil. This is also the case in dewaxing oils with a low ratio of diluent, particularly in the case of oils of high viscosity or of high wax content.

As a consequence of the above discovery, we propose to separate the wax from oils in a plurality of stages employing a higher propane ratio in the first stage than in the subsequent stage or stages. We find that in the first dewaxing stage,

the major portion of the wax, particularly the higher melting point, hard wax is removed and this can be effected in the presence of a high propane to oil ratio of approximately 5 volumes of propane to one volume of the oil. This dilution of the oil is sufficient to give satisfactory filter or settling rates. However, the filtrate will have a high pour point as, for example, 15 or 20 F.

With the removal of the major portion of the wax contained in the oil, the wax concentration in the remaining oil will be lowered sufiiciently as to permit employment of lower propane to oil ratios in the subsequent removal of the remaining wax in the oil. The reduction of the propane to oil ratio causes relatively higher lubricating oil to propane ratio so that the remaining wax in the oil will readily precipitate from the solution. Thus, the oil solvent solution from which a major proportion of the wax has been removed and comprising approximately five volumes of propane to one of oil may be further chilled by evaporating solvent under reduced pressure until only a sufiicient amount remains to dilute the oil and reduce its viscosity. The propane ratio should be reduced until approximately one or one and one-half volumes of propane to one of the oil remains in solution. The oil solvent solution is then digested with the changed conditions of solvent oil ratio and/or temperature until complete equilibrium has been obtained. The digestion of the solution effects wax crystal growth. The solution may then be filtered to remove additional soft wax which has been. precipitated by the reduction of propane to oil ratio and/or by further chilling. If desired, further dewaxing of the filtrate may be accomplished at progressively decreasing propane to oil ratios either at the same temperature or at lower temperatures in subsequent stages. Generally, however, two stages will suffice to produce a lubricating oil when freed of solvent of low pour point.

The adjustment of temperatures and solvent ratios to give a proper balance between the first and second filtrations or separations depends, of course, on the solvent employed and the nature of the stock treated.

It will be observed that in the present discussion of our invention, we intend to include as diluents or solvents also such hydrocarbon fractions as are normally vaporous at ordinary temperature and pressure. Such hydrocarbons include methane, ethane, propane, butane, isobutane and mixtures thereof. These volatile solvents may be obtained by rectification of casinghead gasoline by the so-called stabilization method now conventional in the natural gasoline industry. They may be obtained as the overhead in the stabilization or may be obtained as a side stream product from plates near the top of the stabilizing column. When obtained as overhead vapors, they are liquefied by compression and cooled in the conventional manner and are drawn ofi into pressure chambers where they are maintained in a liquid state until used. A typical analysis of such an overhead fraction is 6.7% ethane, 72.2% propane, 19.9% isobutane and 1.2% normal butane, whereas a side stream product may consist of as high as 98% propane. Such a fraction may be maintained in a liquL'd state at a pressure of approximately 125 lbs. per square inch at a temperature of about 75 F. The predominating hydrocarbon member in this mixture is propane and hereafter when we use the term propane or liquid propane we are .wax which comprises separating the wax by refrigeration in the presence of a diluent in a plurality of stages and in which the solvent to oil ratio is decreased as wax is separated from the oil in the prior stages of operation. The invention has, as one of its features, the use of liquefied normally gaseous hydrocarbon solvents, as liquid propane, as diluents for refrigeration of the oil to precipitate wax and to give good settling and filtration of the solution containing precipitated wax. The invention also includes the employ ment of progressively decreasing temperatures for wax precipitation in the several stages of the process.

More specifically this invention comprises a process for dewaxing lubricating oil stocks wherein the oil is dissolved in a liquefied normally gaseous hydrocarbon solvent, as liquid propane, under pressure sufficient to maintain the solvent in a liquid state, in then reducing the pressure of the oil propane solution containing wax to vaporize a portion of the propane and thus chill the oil to precipitate the wax, in then removing the precipitated wax from the oil propane solution, in subsequently removing a portion of theremaining propane from the oil propane solution and digesting the remaining oil propane solution to effect further precipitation of wax at a lower propane to oil ratio than that accompanying the separation of wax in the first stage, in separating the precipitated wax from the oil propane solution and in finally separating the propane from the oil. As a specific example of the process, we may employ a volumetric propane to oil ratio of 5 to l in the first stage of the process to separate the major portion of the wax from the oil and subsequently separating the remaining wax at the lower propane to oil ratio of l or 1%,; to l. The wax precipitation and separation in the first stage may be effected at a temperature of F. and that in the second stage may be accornplished at a temperature of -40 F., or the separation in both stages may be accomplished at the same temperature of approximately 40 F. If desired, the process may be carried out in three stages of wax separation. In the first stage, the wax may be separated at 0 F. in the presence of volumes of propane to one volume of the oil, in the second stage at a temperature of 40 F. in the presence of 3 volumes of propane and in the third stage at a temperature of 55 F. in the presence of one volume of propane to one of the oil; or the three stages employing volumetric ratios of 5, 3 and 1 volumes of propane, respectively, to one of the oil, may be carried out at the same temperature of say l5 F. The important feature of this invention resides in the use of decreasing volumetric ratios of propane to oil as wax is separated from the solution of oil and propane so as to permit wax which is dissolved in the propane at the higher volumetric ratios to precipitate from solution when reducing the volumetric ratio in the later stages.

Other objects and advantages of our invention will be apparent from the following description of our invention taken from the drawing which refers to a schematic arrangement of apparatus for carrying out the invention:

Referring to the drawing, an asphalt and wax containing oil is taken from tank I and is drawn into line 2 controlled by valve 3 by pump 4 where it meets .a liquefied normally gaseous hydrocarbon solvent such as liquid propane taken from storage tank 5 via line and pump I which forces the liquid propane through valve 8 into line 2. The amount of propane introduced into line 2 will depend upon the character of the oil but should be sufficient to precipitate substantially all of the asphalt present in the oil. This amount may vary from 3 to 8 volumes of propane and upwards to one volume of the oil. If desired, the amount of propane mixed with the oil may be regulated so as to give the proper degree of chilling by evaporation of propane under reduced pressure in the subsequent wax precipitating stages as will be described hereinafter. The mixture of liquid propane and oil containing asphalt and wax is passed through turbulence or mixing coil 9 into decanter or asphalt precipitator I where the asphalt in the oil is precipitated and settles rapidly as a slurry of substantially pure bitumen or hard asphalt containing some oil and propane. A pressure of approximately 125-175 lbs. per square inch and a temperature of about 70 F. to 80 F. is maintained in the decanter II].

Pressures within the above range will be sufficient to maintain the propane in a liquid state at such temperatures. The pressure in decanter It! may be maintained by means of equilibrium line II controlled by valve I2 which connects the decanter III with the high pressure storage tank 5.

The asphalt precipitated from the, oil in decanter It} may be withdrawn via line I4 controlled by valve I as a slurry of substantially pure bitumen containing some oil and propane. This mixture may be treated for removal of propane and reduction of the remaining asphalt to proper specification such as fiash and fire points. This will be readily understood by those skilled in the art. The propane contained in the slurry which may be removed by distillation may be recovered by compression and cooling and returned to propane storage tank 5.

Instead of precipitating and separating the asphalt from the oil in one decanter as described above, the asphalt separation may be carried out countercurrently in several stages. For example, the oil from tank I may be mixed with a propane oil solution of a second stage to precipitate a liquid asphalt, that is, an asphalt containing a substantial amount of oil and this asphalt may then be mixed with fresh propane and passed into the second stage where the oil remaining in the asphalt is dissolved with fresh propane and decanted from the remaining substantially pure bitumen. This solution is then employed to treat the oil from tank I as aforesaid. Likewise, the solution of oil and propane from the first stage may be mixed with further quantities of fresh propane to precipitate additional asphalt from solution.

The overflow from decanter I0 consisting of propane and oil substantially free from the asphaltic materials separated in decanter I 0 but containing wax and other wax-like impurities, is sent through line I6 and pressure reduction valve I! into the first chilling column I8 where s cient propane vaporizes to reduce the temperature of the remaining material to a low temperature sufiicient to precipitate a substantial portion of the wax contained in the oil. The

temperature in chiller I8 is reduced to approximately 0 F. or lower and preferably at a gradual rate, i. e. not in excess of 3 or 4 F. per minute. This may be accomplished by controlling the pressure in chiller I8 by the proper operation of valve 2|! on line I9 and compressor 22 which is connected to the chiller by lines I9 and 2|. The pressure will be gradually lowered in column I8 to about lbs. gauge which corresponds to a temperature of approximately 0 F. If desired, the temperature may be rapidly lowered at a rate of about 10 F. per minute until a temperature of approximately to F. is attained which corresponds to the cloud point or the point where wax begins to precipitate from solution. The mixture may thereafter be gradually lowered to 0 F. at a rate of approximately 3 F. per minute. The propane evaporating in column I8 is withdrawn via line I 9 controlled by valve 20 and passes via line 2I to the suction of compressor 22 where the vapors are compressed, pass through line 23, liquefied in cooler 24 and run down to propane storage tank 5. Y

Due to the fact that sufficient time must be given to gradually chill the solution of oil and propane in column I8 and to make the process continuous, a plurality of chilling columns I8 may be provided and operated alternately. However, when operating a batch process, merely one of such chilling columns will be sufficient. Thus,

the entire charge from decanter I0 may be transferred into the column I8 and the chilling accomplished by controlling the operation of valve 20 on line I9. If the solution of oil and propane entering the chiller I8 does not contain sufficient 1;.

propane to efiect the desired chilling, further quantities of liquid propane may be mixed with the solution entering the chiller to give the desired refrigeration of the oil.

In the preferred operationwhen using proas amixture of 5 volumes of propane to one volume of oil and as the propane is vaporized further quantities of liquid propane are introduced to make up for that vaporized and to maintain the volumetric ratio of 5 to 1. When the temperature in the chiller has been reduced to approximately 0 F., the mixture of propane and oil containing precipitated wax is withdrawn from the bottom of the chiller via line 25 controlled by valve 26 and pumped by pump 27 into the vapor tight wax separator or settler 28. In batch operation, merely one of such settlers will suffice but to make the process contin uous a plurality of these settlers may be employed and operated alternately and thus provide for sufficient settling periods. In order to prevent ebullition in the wax settler during the wax settling operation, pressure is imposed upon the solution of oil. This is accomplished by maintaining pressure within the separator by pump 27. As the chilled mass in the wax separator remains in a non-ebullient state, the wax settles out and is collected by vanes 29 operated by pulley 38 connected to a suitable source of power not shown. Instead of employing settling for separating the precipitated wax, the separation may be accomplished by filtration or centrifuging.

The wax slurry collecting at the bottom of the wax settler is withdrawn via line 3| controlled by valve 32 and treated for removal of residual Cit Lil

propane and oil from the wax such as by heating the slurry to temperatures sufficient to vaporize the propane and oil. The propane may be compressed and cooled and returned to propane storage tank 5. The oil is preferably removed from the wax slurry by washing with fresh propane.

The propane solution of oil containing unprecipitated wax is withdrawn from the separator 28 and passed into line 33 controlled by valve 34 and pumped by pump 35 through line 36 into a second chilling column 31 where the solution is chilled to a temperature of approximately l0 F. by vaporization of propane in a manner similar to that described in chiller l8. It is preferable to vaporize the propane in chiller 3? at a rate not greater than 3 F. per minute. The vaporization of propane in chiller ill is controlled by gradually lowering the pressure by means of valve 39 on line 38 to approximately 0 lbs. gauge which corresponds to a temperature of 40 F. The vaporized propane from chiller 31 passes via line 38 and valve 39 into line 2| to compressor 22, cooler and propane storage tank 5. The vaporization of propane in chiller 37 is continued until approximately one and one-half volumes of propane to one volume ofoil remain in the chiller. This amount of propane is sufficient to dilute the oil and reduce its viscosity so that the precipitated wax may be readily separated by filtration. The chilled mixture is digested for a period of time under the changed conditions of solvent ratio and temperature until complete equilibrium has been attained. The reduction of solvent ratio permits a substantial amount of soft Wax which is soluble in propane to precipitate from solution.

The precipitated oil and propane is withdrawn from the chiller 37 via line 4!! controlled by valve 4i and pumped by pump @2 through line 43 through filter 44 where the precipitated wax is separated from the propane oil solution. The separated wax is withdrawn from the filter via line G5 controlled by valve Q6 and passed to suit-able heating and propane separating apparatus where the vaporized propane may be cornpressed, cooled and returned to propane storage tank 5. The wax free solution of propane and oil is passed through line t! controlled by valve 28 and pumped by pump 49 through line 58 into heater 5| which is provided With mist extractor 52 where the propane present in the oil is vaporized by the aid of steam circulated through the closed steam coil 53. The vaporized propane passes out of the heater through line 54 controlled by valve 55, cooled in cooler 55 and then passes through lines 57, 33 and 2! to compressor 22, cooler 24, into propane storage tank 5. The dewaxed propane free oil passes from heater 55 by means of line 58 controlled by valve 59 to pump 68 which passes the oil into storage tank 6|.

The dewaxed oil may be chemically treated, as, for example, by means of sulphuric acid to remove unsaturated oil and other impurities from the oil which is subsequently Water washed and neutralized with alkali, such as sodium hydroxide and/or clay. The chemical treatment may be performed in the presence of a diluent, such as the propane employed in the dewaxing steps and this operation may be carried out either subsequent to the final wax separation stage or at any of the intermediate dewaxing stages while the solution is in a chilled condition or prior to the Wax separation stages, as, for example, subsequent to the removal of asphalt.

The foregoing is a description of a process as carried out on residual oils or lubricating oil stocks containing both asphalt and wax. Where oils to be treated are substantially free from asphalt, the asphalt precipitating and separating stage is omitted and the solution of propaneand oil is directly treated for Wax removal by introducing the mixture of waxy oil and propane into chilling column IS.

The following is a description of the invention as carried out on one type of oil employing liquid propane as a diluent and internal refrigerant:

An S. A. E. 10 Santa Fe Springs rafiinate, produced by extracting a wax containing oil with a mixture of 70% liquid sulphur dioxide and 30% benzene, and containing approximately 30% by weight of Wax was mixed with approximately 9 volumes of propane and passed into decanter l8. A temperature of approximately F. and a pressure of about 150 lbs. per square inch was maintained in decanter I8. In chilling column l8, suiiicient propane was vaporized to reduce the temperature of the mixture to approximately 19 F. to precipitate a substantial portion of the wax. The mixture of precipitated wax, oil and propane was permitted to digest under pressure for approximately twenty minutes and settle, approximately 5 volumes of propane to one volume of the oil being maintained during the wax settling period, in settler 25. The settled precipitated wax was withdrawn and then Washed with further quantities of propane to remove any oil present in the wax. The quantity of wax recovered comprised approximately 25% by weight of the charge and had a melting point of approximately 130 F. Ubbelohde. The oil in approximately 500 volume percent of propane having a pour point of approximately 20 F was then chilled to approximately 42 F. by vaporization of propane. Approximately one volume of propane remained in the oil. This chilling caused the remaining wax to precipitate from solution. The mixture of propane, oil and precipitated wax was then digested under pressure for about fifteen minutes and Was then passed through a filter Where the precipitated wax was separated from the oil propane solution. This wax was also washed with further quantities of propane to remove any contained oil in the wax. The melting point of this wax approximated 105 F. Ubbelohde. The filtrate Was then de-propanized by evaporation. The wax free oil showed a pour point of approximately l5 F.

As a modification of the above, the wax separation process may be accomplished in three stages of chilling and wax separation, for example, the first wax may be precipitated at a temperature of 0 F. and filtered in the presence of approximately 590 volume percent of propane. The propane oil solution may then be chilled to approximately 4=0 F. and filtered in the presence of approximately 300 volume percent propane, after which the propane oil solution may be chilled to 55 F. by maintaining a vacuum in the chiller and filtered in the presence of volume percent of propane. If desired, the wax separation or filtration in the three stages may be accomplished at the same temperature of approximately l5 F., employing, however, 500, 300 and its volume percent of propane, respectively, during the filtration stages.

In some instances, We find it advantageous to precoat the plates of the filter with such filter aids as diatomaceous earth, fullers earth, clay,

wood flour or sawdust, prior to filtration. By depositing a thin layer of any of the foregoing materials upon the filter plates prior to passing the chilled mixture of propane and oil containing precipitated wax through the filter, we are sometimes able to obtain a more thorough separation of the precipitated wax from the oil dissolved in propane. In carrying out this type of operation, we first mix a small quantity of the precoating materials, such as diatomaceous earth, etc., with liquid propane and pass this mixture through the filter. The precoating substance suspended in the liquid propane deposits itself in a thin layer over the filter plate and the propane is withdrawn from the filter press as a clear filtrate. The chilled oil dissolved in liquid propane carrying precipitated wax in suspension is now forced through the filter press and the precoating materials present on the filter plates aid in separating the wax from the propane solution of oil. While we may employ any of the foregoing materials as precoating substances for the filter press, we have found wood flour to be especially well adapted for this purpose. If desired, the filter aids may be admixed with the propane solution of oil either prior to chilling or subsequent thereto and prior to passage of the chilled mixture through the filter press.

The use of wax crystallization inhibitors or nodifieis, such as condensation products of aromatics with paraffinic hydrocarbons produced by a Friedel Craft reaction between chlorinated parafiin wax and an aromatic hydrocarbon, is sometimes helpful in producing a wax precipitate which is more easily filtered from the solvent solution of oil. The wax crystallization inhibitor functions in such manner as to promote crystal growth in the present instance. The crystallization inhibitor may be added to the waxy oil or to the solution of the waxy oil in the solvent at any stage during the chilling operation but for the best results, it is usually preferable to add the crystallization modifier before the chilling or concentration of the solvent is begun in preparation for a given filtration operation. For instance, the crystallization modifier may be added to the original mixture of oil and propane at atmospheric temperature or it may be added after the first stage of wax separation before further concentration of solvent is effected as explained above.

In place of the above condensation products, We may use other asphaltic, pseudo-asphaltic or colloidal bodies, such as heavy residual oils, asphalt, cracked residues or high molecular weight fractions obtained from these by distillation or solvent extraction. We may also add as wax crystallization inhibitors high molecular weight wax bodies and oxidized acidic bodies, metal soaps of organic acids and the like.

It is to be understood that the above description is merely illustrative of preferred embodiments of our invention of which many variations may be made by those skilled in the art without departing from the spirit thereof.

We claim:

1. A process for separating wax from oils containing the same which comprises mixing said oil with a hydrocarbon solvent which at elevated temperatures completely dissolves both oil and wax and which at dewaxing temperatures com-- pletely dissolves oil but only dissolves small but appreciable amounts of wax, chilling the oil solvent solution to precipitate wax, separating the precipitated wax from the oil solvent solution in a plurality of stages and at decreasing solvent to oil ratios.

2. A process as in claim 1 in which the solvent comprises a liquefied normally gaseous hydrocarbon.

3. A process as in claim 1 in which the solvent comprises liquid propane.

4.-A process for separating wax from oils containing the same which comprises mixing said oil with a hydrocarbon solvent which at elevated temperatures completely dissolves both oil and wax and which at dewaxing temperatures completely dissolves oil but only dissolves small but appreciable amounts of wax, chilling the oil solvent solution to precipitate wax, separating the precipitated wax from the oil solvent solution, separating a portion of the solvent from the oil solvent solution to effect further precipitation of wax, separating the last mentioned precipitated wax from the oil and remaining solvent and separating the remaining solvent from the oil.

5. A process for separating wax from oils containing the same which comprises mixing the oil with a liquefied normally gaseous hydrocarbon solvent under pressure, reducing the pressure on the oil solvent solution to vaporize a portion of the solvent to chill the oil and precipitate wax, separating the precipitated wax from the oil solvent solution, separating further quantities of solvent from the oil solvent solution to. permit further quantities of Wax to precipitate from solution, separating said last mentioned precipitated wax from the oil in the presence of the reduced quantity of solvent and separating the remaining solvent from the oil.

6. A process for separating Wax from oils containing the same which comprises mixing said oil with liquid propane under pressure sufiicient to maintain said propane liquid, reducing the pressure and vaporizing a portion of the propane to chill the oil and precipitate wax, separating the precipitated wax from the oil propane solution, vaporizing further quantities of propane from the oil propane solution to reduce the concentration of propane in the oil propane solution and thus precipitate further quantities of wax, separating said last mentioned precipitated wax from the oil and propane and separating the propane from the oil.

7. A process for separating wax from oil containg the same which comprises mixing said oil with a hydrocarbon solvent which at elevated temperatures completely dissolves both oil and wax and which at dewaxing temperatures completely dissolves oil but only dissolves small but appreciable amounts of wax, chilling the oil solvent solution to a wax precipitating temperature to preciptate a substantial portion of the wax, separating said precipitated wax from the oil and solvent, lowering the concentration of solvent in the oil to permit further quantities of wax to precipitate from solution and reducing the temperature to a still lower wax precipitating temperature to precipitate further quantities of wax, separating said precipitated wax from the oil in the presence of said lower concentration of solvent and separating the said solvent from the oil.

8. A process as in claim 7 in which the solvent comprises a liquefied normally gaseous hydrocarbon.

9. A process as a claim 7 in which the solvent comprises liquid propane.

10. A process for separating wax from oil containing the same which comprises mixing said oil with liquid propane under pressure, reducing the pressure of the oil propane solution to vaporize a portion of the propane to chill the oil and thus precipitate the wax, separating said precipitated wax from the oil and remaining propane, reducing the pressure further to vaporize further quantities of propane and thus chill the oil to a lower temperature than said first chilling operation to precipitate further quantities of wax, separating the precipitated wax in the presence of a lower concentration of propane and separating the propane from the oil.

11. A process for separating wax from oil containing the same which comprises mixing said oil with a liquefied normally gaseous hydrocarbon under superatmospheric pressure, vaporizing a portion of the solvent under reduced pressure to chill the oil and precipitate a portion of the wax and to leave a volumetric ratio of solvent to oil in excess of l to 1 removing the precipitated wax from the oil and solvent, vaporizing a further portion of the solvent to chill the oil to a lower temperature to precipitate a further portion of wax and removing the precipitated wax in the presence of approximately 1 to 1 volumesof solvent to one of the oil and subsequently separating the solvent from the oil.

12. A process as in claim '7 in which the solvent is substantially liquid propane.

13. The process of removing wax from lubricating oils comprising dissolving the oil and wax in a liquefied normally gaseous diluent, cooling the solution to cause a major portion but less than all of the wax to precipitate, separating the precipitated wax, removing a portion but less than all of the diluent from the partially dewaxed oil solution and simultaneously chilling said oil solution to a lower temperature to cause precipitation of the remaining wax, separating the wax precipitated at said lower temperature from the oil solution, and removing diluent from said last mentioned oil solution.

14. A process as in claim 13 in which the diluent comprises a liquefied normally gaseous hydrocarbon.

15. A process as in claim 13 in which the diluent comprises liquid propane.

ULRIC B. BRAY. DONALD E. CARR. 

